This book contains annotated translations of 540 passages in Commentary on Shuowen Jiezi, which are devoted to explaining meanings of the characters used as radicals. The translation work was launched as a first step for enhancing proper understanding of the book, Shuowen Jiezi. The translation not only covers the passages from the original text but also covers annotations to those passages by Duan Yucai, an eminent scholar of Qing Dynasty period and the most recognized authoritative figure in the study of annotations to Shuowen Jiezi.Shuowen Jiezi is the earliest extant lexicography in China, complied circa A.D. 100 by a scholar named Xu Shen, whose exact dates of birth and death are unknown. The book consists of 15 chapters, giving explanations on 9,353 characters. Xu categorized all these characters into 540 groups of distinctive meaning, and made each group represented by a character, which is called 'Radical'. Therefore, the body of Radicals forms a core structure of the whole text of Shuowen Jiezi: it functions as a network in which all the characters dealt with in the text are related to each other, and also as a source from which 'extensions and developments in meanings of characters' can be detected.